[CASSANDRA-9425] Make node-local schema fully immutable

• Type: Sub-task
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 4.0-alpha1, 4.0
• Assignee: Aleksey Yeschenko
• Reporter: Aleksey Yeschenko

Authors

Aleksey Yeschenko

Reviewers

Sylvain Lebresne

• Created: 19/May/15 16:37
• Updated: 15/May/20 08:01
• Resolved: 27/Jan/17 22:22

Description

The way we handle schema changes currently is inherently racy.

All of our SchemaAlteringStatement s perform validation on a schema state that's won't necessarily be there when the statement gets executed and mutates schema.

We should make all the *Metadata classes (KeyspaceMetadata, TableMetadata, ColumnMetadata, immutable, and local schema persistently snapshottable, with a single top-level AtomicReference to the current snapshot. Have DDL statements perform validation and transformation on the same state.

In pseudo-code, think

public interface DDLStatement
{
    /**
     * Validates that the DDL statement can be applied to the provided schema snapshot.
     *
     * @param schema snapshot of schema before executing CREATE KEYSPACE
     */
    void validate(SchemaSnapshot schema);
 
    /**
     * Applies the DDL statement to the provided schema snapshot.
     * Implies that validate() has already been called on the provided snapshot.
     *
     * @param schema snapshot of schema before executing the statement
     * @return snapshot of schema as it would be after executing the statement
     */
    SchemaSnapshot transform(SchemaSnapshot schema);
}

Issue Links

• incorporates: CASSANDRA-9665 Improve handling of UDF and UDA metadata
• incorporates: CASSANDRA-9712 Refactor CFMetaData
• incorporates: CASSANDRA-9677 Refactor KSMetaData
• is duplicated by: CASSANDRA-9449 Running ALTER TABLE cql statement asynchronously results in failure
• is duplicated by: CASSANDRA-10250 Executing lots of schema alters concurrently can lead to dropped alters
• is duplicated by: CASSANDRA-13061 C* driver hangs forever in case of concurrent CREATE TABLE IF NOT EXISTS
• is related to: CASSANDRA-13164 eclipse-warnings on CASSANDRA-9425